Identifying the mechanism of an arrhythmia based on its intracardiac electrograms has become a common challenge to both implantable cardiac defibrillators (ICDs) and the physicians taking care of patients with ICDs. These devices, which are primarily designed to deliver therapy for life-threatening ventricular arrhythmia, frequently deliver inappropriate shocks for supraventricular tachycardias. These inappropriate shocks constitute a significant source of physical and emotional distress for patients, cause early ICD battery depletions, and generate a huge financial burden on the health system.
Inappropriate electroshocks from implanted cardiac defibrillators constitute a significant source of physical and emotional distress on the patients and an unnecessary expense for the health system. Early generations of implantable cardiac defibrillators operated with an incidence of inappropriate electroshocks as high as 20 to 40%. Tanaka S., An Overview Of Fifth-Generation Implantable Cardioverter Defibrillator, Ann Thorac Cardiovasc Surg., 4:303–311 (1998). Following the introduction of dual-chamber implantable cardiac defibrillators, however, the overall success for delivering appropriate electroshocks increased to 86–100%, while the successful incidence for the treatment of ventricular arrhythmias reached 97–100%.
The incidence of inappropriate electroshocks in response to supraventricular tachycardias, however, remains a problem. This problem is especially severe for discriminating between supraventricular tachycardias having 1:1 antegrade conduction and ventricular arrhythmias having 1:1 retrograde conduction. Thompson et al., Ventriculoatrial Conduction Metrics For Classification Of Ventricular Tachycardia With 1:1 Retrograde Conduction In Dual-Chamber Sensing Implantable Cardioverter Defibrillators, J Electrocardiol., 31:152–156 (1988)
In an attempt to solve this problem, those skilled in the art have attempted using various mathematical algorithms to utilize the quantitative aspects of the ECG with variable success. Specifically, the morphology of a shocking electrogram may be compared to a sinus beat template. Gold et al., A New Defibrillator Discrimination Algorithm Utilizing Electrogram Morphology Analysis, Pacing Clin Electrophysiol. 1999;22:179–182 (1999) Additionally, stability criteria may be employed to distinguish between atrial fibrillation and ventricular arrhythmia. Barold et al., Prospective Evaluation Of New And Old Criteria To Discriminate Between Supraventricular And Ventricular Tachycardia In Implantable Defibrillators, Pacing Clin Electrophysiol., 21:1347–1355 (1998); and Schaumann et al., Enhanced Detection Criteria In Implantable Cardioverter-Defibrillator To Avoid Inappropriate Therapy, Am J Cardiol., 78:42–50 (1996). In comparison, discrimination between sinus tachycardia and ventricular arrhythmia may be determined by the employment of sudden onset criteria. These approaches have reduced the rate of inappropriate electroshocks, but continue to remain at approximately 11%. Schaumann et al. (supra).
The ability to reduce or avoid all inappropriate electroshocks from implantable cardiac defibrillators would have a beneficial effect on the physical and emotional state of patients with defibrillators as well as reduce the cost of health care. Clearly, what is needed in the art is a method and a device to prevent the misinterpretation of cardiac electrical signals and avoid the delivery of inappropriate electroshocks.